# Listbuilding via API Key

Endpoints for adding and removing subscribers using an API key–based authentication model.
These operations are optimized for secure listbuilding scenarios where full API authentication is not required.

## Signin

 - [POST /subscriber/signin](https://developers.klicktipp.com/listbuilding-api/listbuilding-via-api-key/api.subscriber.signin.md): Creates or updates a contact and associates the tag linked to the API key.

Notice: On success, the endpoint returns a system-generated redirect URL depending on the opt-in configuration in KlickTipp.

For Double Opt-in, the URL points to a pending page indicating that email confirmation is required.

For Single Opt-in, the URL points to a final thank-you page.

The client may use this URL for optional redirection; the API itself does not perform any redirect.

## Signoff

 - [POST /subscriber/signoff](https://developers.klicktipp.com/listbuilding-api/listbuilding-via-api-key/api.subscriber.signoff.md): Unsubscribes a contact via the API key and prevents further communication.

## Signout

 - [POST /subscriber/signout](https://developers.klicktipp.com/listbuilding-api/listbuilding-via-api-key/api.subscriber.signout.md): Removes the tag of a contact associated with the API key.